Group III-V compound semiconductors such as GaN and AlGaN are widely used for optoelectronics, electronic devices and the like, owing to many advantages such as, for example, a wide and easily adjustable band gap energy.
In particular, light-emitting devices such as light-emitting diodes or laser diodes using group III-V or II-VI compound semiconductors may realize various colors of light such as, for example, red, green, and blue light, as well as ultraviolet light, via the development of device materials and thin-film growth technique, and may also realize white light having high luminous efficacy via the use of a fluorescent material or by combining colors. These light-emitting devices have advantages of low power consumption, a semi-permanent lifespan, fast response speed, good safety, and eco-friendly properties compared to existing light sources such as, for example, fluorescent lamps and incandescent lamps.
Accordingly, the application of light-emitting devices has been expanded to a transmission module of an optical communication apparatus, a light-emitting diode backlight, which may substitute for a cold cathode fluorescent lamp (CCFL) constituting a backlight of a liquid crystal display (LCD) apparatus, a white light-emitting diode lighting apparatus, which may substitute for a fluorescent lamp or an incandescent bulb, a vehicle headlight, and a signal lamp.
A light-emitting device is provided with a light-emitting structure, which includes a first conductive semiconductor layer, an active layer, and a second conductive semiconductor layer, and a first electrode and a second electrode are respectively disposed on the first conductive semiconductor layer and the second conductive semiconductor layer. The light-emitting device emits light having energy determined by the inherent energy band of a constituent material of the active layer in which electrons injected through the first conductive semiconductor layer and holes injected through the second conductive semiconductor layer meet each other. The light emitted from the active layer may be changed depending on the composition of the constituent material of the active layer, and may be blue light, ultraviolet (UV) light, deep-UV light, or the like.
FIG. 1 is a view illustrating a light-emitting device of the related art.
The light-emitting device of a vertical type illustrated in FIG. 1, a light-emitting structure 120, which includes a first conductive semiconductor layer 122, an active layer 124, and a second conductive semiconductor layer 126, is disposed on a second electrode 136, and a first electrode 132 is disposed on the first conductive semiconductor layer 122.
In the light-emitting device of the related art, in which the active layer 124 emits light, the light emitted from the active layer 124 may be absorbed by the first electrode 132, which may deteriorate the efficiency of extraction of light.